Laminated glazing with coloured reflection and high solar transmittance suitable for solar energy systems

ABSTRACT

Laminated and etched glazing unit for architectural integration of solar energy systems comprising a substrate delimited by two main faces and a multi-layered interference filter also delimited by two main faces, one main face of said substrate being adapted to be in contact with an incident medium, the other main face being in contact with a main face of said interference filter, the other main face of said interference filter being adapted to be in contact with an exit medium; said incident medium having a refractive index n inc =1, said substrate having a refractive index n substrate  defined as follows: 1.45≦n substrate ≦1.6 at 550 nm, and said exit medium being defined as follows 1.45≦n exit ≦1.6 at 550 nm; and wherein said unit is designed in such a way that the following requirements are met: 1a) The saturation of the colour, given by C* ab =√(a*) 2 +(b*) 2 , according to the CIE colour coordinates L*, a* and b* under daylight illumination CIE-D65 is higher than 8 at near-normal angle of reflection, except for grey and brown. 1b) The visible reflectance at near-normal angle of reflection R vis  is higher than 4%. 1c) The variation of the dominant wavelength λ MD  of the dominant colour MD of the reflection with varying angle of reflection Θ r  is smaller than 15 nm for Θ r &lt;60°. 1d) The total hemispherical solar transmittance at near-normal incidence is above 80%.

FIELD OF THE INVENTION

The invention deals with coloured laminated glazing suitable for solarenergy systems offering architectural integration of solar energysystems, e.g. as solar active glass facades.

DEFINITIONS

Direct Transmittance

If parallel beams of radiation incident on a surface, an interface, or aspecimen result in transmitted parallel beams, the transmittance isconsidered as direct. This is the case e.g., for flat surfaces orinterfaces.

Diffuse Transmittance

If parallel beams of radiation incident on a surface, an interface, or aspecimen result in a more or less wide angular distribution oftransmitted beams, the transmittance is considered as diffuse. This isthe case e.g., for rough surfaces or interfaces, or for specimens ofgranular structure.

In general, the diffuse transmittance depends on the angle of incidenceand the wavelength X of the radiation. If the angle of incidence is notexplicitly mentioned, commonly normal incidence is assumed.

Total Hemispherical Transmittance

The total hemispherical transmittance is obtained by the sum of directtransmittance and diffuse transmittance.

T _(total) =T _(direct) +T _(diffuse)

In general, the total hemispherical transmittance depends on the angleof incidence and the wavelength λ of the radiation. If the angle ofincidence is not explicitly mentioned, commonly normal incidence isassumed.

Solar Transmittance T_(sol)

Given a calculated or measured spectrum of the total hemisphericaltransmittance of a sample T(λ), the solar transmittance T_(sol) isobtained by integration with the solar spectrum I_(sol)(λ):

$T_{sol} = \frac{\int{{{T(\lambda)} \cdot {I_{sol}(\lambda)}}{\lambda}}}{\int{{I_{sol}(\lambda)}{\lambda}}}$

where usually the solar spectrum at air mass 1.5 (AM1.5) is employed asintensity I_(sol)(λ).

Visible Reflectance R_(vis)

The visible reflectance R_(vis) is a measure for the brightness of asurface as it appears to the human eye under certain illuminationconditions. A white surface or a perfect mirror exhibits 100% visiblereflectance, coloured or grey surfaces less. The determination of thevisible reflectance R_(VIS) is based on the photopic luminous efficiencyfunction V(λ) and depends on the choice of the illuminant I_(ILL)(λ):

$R_{vis} = \frac{\int{{{R(\lambda)} \cdot {I_{ILL}(\lambda)} \cdot {V(\lambda)}}{\lambda}}}{\int{{{I_{ILL}(\lambda)} \cdot {V(\lambda)}}{\lambda}}}$

where R(λ) is the simulated or measured hemispherical reflectance of thesample.

Angle of Reflection

The angle of reflection θ_(r) is the angle formed by a ray of lightreflected from a surface and a line perpendicular to the surface at thepoint of reflection. Here θ₁ and θ_(t) correspond respectively to theincidence and transmission angles.

Refractive Index and Extinction Coefficient

When light passes through a medium, some part of it will always beabsorbed. This can be conveniently taken into account by defining acomplex index of refraction N:

N=n−ik   [1]

where the real part n (refractive index) indicates the phase speed,while the imaginary part k (extinction coefficient) indicates the amountof absorption loss when the electromagnetic wave propagates through thematerial.

Antireflection

A treated surface is considered as antireflective when the solartransmittance of a light beam at near-normal incidence is higher thanfor an untreated surface.

CIE 1931 XYZ Colour Space

The International Commission on Illumination (CIE, CommissionInternationale d′Eclairage) described how to quantify colours [2]. Allexisting colours can be represented in a plane and mapped by Cartesiancoordinates, as shown in the CIE Chromaticity Diagrams. Thequantification is based on the 1931 CIE Colour Matching Functions, x(λ),y(λ), and z(λ), which reflect the colour sensitivity of the human eye.These functions depend to some extent on the width of the observationfield (we will use the functions for an opening angle of 2°).

CIE 1976 (L*, a*, b*) Colour Space (or CIELAB)

CIE L*a*b* is the most complete colour model used conventionally todescribe all the colours visible to the human eye. It was developed forthis specific purpose by the International Commission on Illumination(Commission Internationale d'Eclairage). The three parameters in themodel represent the lightness of the colour (L*, L*=0 yields black andL*=100 indicates white), its position between magenta and green (a*,negative values indicate green while positive values indicate magenta)and its position between yellow and blue (b*, negative values indicateblue and positive values indicate yellow).

Dominant Colour

The dominant wavelength of a colour is defined as the wavelength of themonochromatic stimulus that, when additively mixed in suitableproportions with the specified achromatic stimulus, matches theconsidered colour stimulus [3]. Thus any colour can be related to amonochromatic dominant colour MD defined by its wavelength X,D.

Colour Saturation

The colour saturation is a measurement of how different from pure greythe colour is. Saturation is not really a matter of light and dark, butrather how pale or strong the colour is. The saturation of a colour isnot constant, but it varies depending on the surroundings and what lightthe colour is seen in and is given by:

C* _(ab)=√(a*)²+(b*)²

where a* and b* are the CIE colour coordinates under daylightillumination CIE-D65.

STATE OF THE ART

The acceptance of solar energy systems as integrated elements of thebuilding's envelope is mainly limited by their unpleasant visual aspect.They are often considered as technical components to be hidden andconfined to roof-top applications, where they are less visible and haveless impact on the architectural design [4]. The development ofbetter-looking solar systems could open up new perspectives for thearchitectural integration of solar energy systems, e.g. as solar activeglass facades. One solution is to apply a coloured interferential thinfilm to the inner side of the glazing of the solar system. The coatingreflects a colour, thus hiding the technical part of the solar device,but transmits the complementary spectrum. Coloured glass panes based ondielectric thin films multi-depositions have been demonstrated to be ofspecial interest for solar thermal collectors [5-8] and has been thesubject to a PCT application in 2004 [9]. The invention disclosed inthis PCT application had, however, some weaknesses dealing with:

-   -   The security: the invention considered the use of non-tempered,        non-laminated glazing that did not fulfil the security        requirements for facade installation. Therefore the coloured        designs calculated for single glazing (exit medium air        n_(exit)=1) are not suitable for laminated glazing (exit medium        polymer 1.45≦n_(exit)≦1.6 at 550 nm).    -   The colour stability: in the context of the 2004 PCT        application, the colour was based on quarter wave interference        stacks exhibiting narrow reflection peaks. By limiting the        number of individual layers and choosing the refractive indices        of the involved materials, reasonable amplitudes of the        reflection peak were obtained, thus providing excellent solar        transmittance to the coating. However, as the narrow reflection        peak shifts to smaller wavelength with increasing angle of        reflection, the former developed colours (except blue) were        dependant on the angle of vision/observation/reflection. Example        1 presents a green design which shifted to blue for increasing        angles of observation (see FIG. 1, FIG. 2 and Table 1).    -   The industrial scale production: relatively thick (>100 nm) SiO₂        layers were needed in the coating stacks, thus limiting the        production speed of coloured glasses on industrial scale.

The PCT application also referred to the possibility of applying asurface treatment (hot patterning, acid etching, sand or stoneprojections . . . ) on the outer side of the collector glazing to inorder to create a diffuse light transmittance. This treatment has theeffect of reinforcing the masking effect of the solar device technicalparts, preventing glare effects and producing mat surfaces that are inhigh demand in today's architecture. Amongst available diffusive surfacetreatments, acid etching is undoubtedly the most suitable and mostwidely used treatment at industrial level. Historically, acidic etchingtreatments of glasses are performed by usingfluoridric-acid-based-solutions [10]. Fluoridric acid is a strongchemical agent responsible of various problems in terms of safety,health of workers and environmental pollution. For this reason, the useof buffered solutions (in which a part of the fluoridric acid isreplaced by fluoride salts such as ammonium bifluoride) [11-13] orsolutions based on fluoride salts [14-15], less aggressive and moreenvironmentally friendly, are becoming more common.

GENERAL DESCRIPTION OF THE INVENTION

The problems mentioned in the previous chapter have been solved with thepresent invention which relates to a solar glazing unit as defined inthe claims. The present innovation deals with coloured laminated glazing(preferably, but not exclusively, made of glass) with enhanced maskingeffect, angular colour stability, energetic performances and mechanicalstability. The coloured laminated glazing system is schematised in FIG.3 and can be described as the combination of:

-   -   An encapsulated coloured interferential multi-layered coating,        deposited on the back side of the outer glass (FIGS. 3 a and 4        a), on the back or the front side of a polymeric film which is        encapsulated between two glass panes (FIGS. 3 b and 4 b) or on        the front side of the inner glass (FIGS. 3 c and 4 c).    -   A textured or non-textured diffusive outer surface    -   An optional anti-reflection coating applied on the back-side of        the inner glass for thermal or PVT applications.

Whereas solar thermal or PVT systems are mounted behind or directlyglued to the laminated glazing, PV systems are totally integrated intothe laminated glazing.

1. Coloured Coating

The choice of the substrate on which the coloured coating is depositedis of main importance. In order to ensure a maximal efficiency of thesolar energy system, the substrate has to present a high solartransmittance, thus limiting the possibilities to solar roll glass,extra-white float glass (very low iron-content) or polymeric materialssuch as polyethylene terephthalate (PET), polyethylene naphtalate (PEN),fluorocarbon polymer (PFA, FEP, ETFE, PTFE . . . ) and so on. Thesurface flatness is also a critical issue, especially for facadeapplications. As no colour variation of the interferential coatingshould be visible, extra-white float glass and polymer materials, givingmore freedom in the choice of the glass nature, are preferred to solarroll glass for the deposition of the coloured coating.

The coloured coating consisting in multilayer interferential stacks oftransparent layers has to be of high solar transmittance T_(sol). Thus,as absorption in the coating should be minimised, dielectric oxides arepreferably chosen. Among the various possibilities, materials such asSiO₂, Al₂O₃, MgO, ZnO, SnO₂, HfO₂, Nb₂O₅, Ta₂O₅ and TiO₂ are for exampleperfectly suitable for the invention described here.

The visible reflectance R_(vis) is the percentage of light striking theglazing that is reflected back and provides information on the maskingcapability of the glazing. This value has then to be high enough topermit a good masking effect of the solar energy system technical partsbut low enough to ensure a good solar transmittance. Good compromiseshave then to be found between masking effect and performances of thesolar device. In the context of the invention, R_(vis) has to be higherthat 4%.

The intensity of the colour is given by its saturation expressed by:

C _(ab)=√(a*)²+(b*)²

where a* and b* are CIE colour coordinates under daylight illuminationCIE-D65. In order to provide well-visible colours, the colour saturationhas to be higher than 8 at near-normal angle of reflection. Exception ismade for grey and brown which correspond respectively to stronglydesaturated cold and warm colours.

Concerning the colour stability, improvements have been brought here ascompared to the 2004 PCT application by modifying the quaterwaveinterference stacks in order to get asymmetric designs. The consequenceof such modifications is the obtaining of reflectance curvescharacterised either by a large single reflection peak or by severalsmall reflection peaks. Then, the multilayer coating reflects a colourwhich is defined, as a function of the shape of the reflectance curve:

-   -   Either by the wavelength of the maximum intensity of a single        reflectance peak situated in the visible part of the solar        spectrum. For example, FIG. 5 represents a reflectance curve at        normal incidence (angle of vision of 0°) with a maximal        intensity at λ_(max)=570 nm which corresponds to a yellow-green        dominant colour for the coating.    -   Or by the combination of the wavelengths of 2 or more        reflectance peaks situated in the visible spectral region. For        example, FIG. 6 shows a reflectance curve at normal incidence        with 3 peaks in the visible part of the spectrum and        respectively situated at 413 nm, 534 nm and 742 nm. The        resultant dominant colour of the considered coating is situated        at λ=500 nm (green).

With increasing angle of vision most features of the spectra shift tosmaller wavelengths, inducing a modification of the position of λ_(max)and thus of the dominant colour of the coating. As example, thereflectance curves obtained for both yellow-green and green coatings atvarious angles of reflection θ_(r) (from 0° to 85°) are given in FIG. 7(a) and (b) respectively.

Providing coloured glazing with good angular colour stability is of highimportance for building integration. Strong efforts have then been madein order to avoid or limit the colour variations. The principle of thecolour stability can be explained as follows. Generally, the colour M ofa layer can be regarded as a mixture of several colours whatever theshape of its reflectance curve. For more clarity, the explanations willbe given for a fictive coloured layer characterized by two reflectionpeaks, in the visible part of the solar spectrum, whose wavelengths andcolours are respectively λ₁, C₁ and λ₂, C₂ (see FIG. 8 a). The colour Mis defined by a dominant colour M_(D) whose wavelength λ_(MD) comprisedbetween λ₁ and λ₂, its position depending on the relative intensity ofboth reflection peaks (see FIG. 8 b). With increasing angles of visionthe reflection peaks shift to shorter wavelengths. The shift of C₁ toC_(1′) has to be compensated by an equivalent shift of C₂ to C_(2′) aswell as a modification of the relative intensity of both peaks in orderto conserve the position of the point M. At least, the point M has to bekept on the on the colour segment defined by the line MM_(D). In thatlast case, the dominant colour of the coating remains the same. Thiscompensation can be achieved by choosing carefully the nature and thethickness of the materials of the individual layers constituting theinterferential coloured coating stack. This principle can beextrapolated to more complex designs characterised by more than twopeaks of reflection (see FIG. 9).

Green coloured designs based on this principle are given in Examples 2,3 and 4 (see FIGS. 10, 11, 12, 13, 14, 15 and tables 2, 3 and 4). The(x,y) colour coordinates under CIE-D65 illuminant, the visiblereflectance R_(vis), the solar transmittance T_(sol), the dominantwavelength λ_(MD) and colour M_(D) and colour saturation C_(ab)* ofthose 3 coatings are given for different angles of reflection.Corresponding graphical presentations of colour variations are alsoshown for each design. For each design, only small variations in colourand in reflectance (especially for θ_(r) up to 60°) are observed incombination with high solar transmittances (above 80% up to 60°). Thevariation of the wavelength of the dominant colour observed for thesecoating designs (9 nm of variation between 0° and 60° for Example 2) isalmost 4 times lower than for the 2004 PCT application design (Example1).

Another advantage here as compared to the 2004 PCT application [6], isthat the relatively thick SiO₂ coatings have been replaced by otheroxides with higher deposition speed. As a matter of facts, multilayerinterferential stacks are deposited on industrial scale by in-linemagnetron sputtering. For low cost production, the number of sub-layersand the thickness of the individual layers have to be limited.

Other examples of coating designs with various colours in reflection(blue, yellow-green, yellowish-orange, grey and brown) are given inExamples 5 to 9 (see FIGS. 16 to 25 and tables 5 to 9).

2. Diffusive Surface

A diffusive surface treatment is applied on the outer surface of thecoloured laminated glazing. The glass substrate can either beextra-white float glass or solar roll glass. Extra-white float glasspresents the advantage of having a better flatness and will be preferredfor facade applications. Both types of glass are also commerciallyavailable with a wide variety of textures and patterns applied on theouter surface. This kind of glass can be used in order to add somerelief and get closer to tiles appearance in case of roof applications.

The etching treatment is applied in order to create diffuse lighttransmittance which reinforces the masking effect of the colouredfilter. It also presents the advantage to create mat surfaces oftendesired by architects and to prevent glare effects.

By choosing appropriate compositions of the etching solution, favourablemicro/nano-structures on the treated glass surface can also give rise toanti-reflection properties. For example, the treatment of glass surfacesby acid etching in buffered solutions [13] leads to a particularstructure combining micrometric islands with nanometric openings, bothuniformly distributed. The resulting low reflectance glass surfaces thusobtained are perfectly suitable for the solar applications describedhere.

Based on literature [14-15], etching solutions composed of several ofthe following components have been developed: ammonium bifluoride (ABF),water (H₂O), isopropanol (IPA), sugars (sucrose, fructose, etc.). Thesesolutions are particularly effective over a wide range of compositionsand for treatment times lower than 20 minutes.

Examples of effective solutions with range of reasonable concentrationsare given below:

-   -   Solution 1: ABF/IPA/water mixture with the following proportions        10-30 wt. %/20-40 wt. %/balance.

Solution 2: ABF/sucrose/water mixture with the following proportions15-25 wt. %/15-40 wt. %/balance.

Excellent transmittances are obtained for the treated glass surfacesthanks to anti-reflective properties. The measured hemispherical normaltransmittance of the treated glass surfaces is about 95% as regards to92% for an untreated glass (see FIG. 26).

FIGS. 27 a) and b) present SEM pictures of glass surfaces respectivelystructured by an ABF/IPA-based etching solution (ABF/IPA/H₂O=30/10/60)and by an ABF/sucrose-based etching solution (ABF/sucrose/H₂O=18/18/64).Both pictures have been taken for the same etching time (15 min) and atsame magnification. In the first case (FIG. 27 a), the surface isrelatively smooth and presents some micro-scale protrusions and furrowsarising from the junction of nano-holes which are present on the entiresurface. In the second case (FIG. 27 b), the surface features a muchrougher structure and is densely covered with some kind of pyramids.These pyramids have a height around 10 μm, are defined by differenttypes of polygons as their base area whose dimensions are often around100 μm to 120 μm and have pronounced nano-structured side walls. Themeasured gain in solar transmittance can then be explained byanti-reflective properties resulting from micro-scale patterning incombination with a nano-scale roughness modification.

3. Tempering and Lamination

After coating deposition and etching, the different glass panes aretempered. There is no restriction to perform this thermal treatment, asboth coloured coatings (made of oxides) and diffusive surfaces (mainlySiO₂) present very good thermal stabilities.

Then, glass panes and if necessary other elements (coated polymericfilm, crystalline silicon cells . . . ) are joined together bylamination. Laminating polymers are preferably, but not exclusivelyelastomer cross-linking products such as EVA (Ethylene-Vinyl-Acetate) orthermoplastic products such as PVB (Polyvinyl Butyral). These productsare characterised by high solar transmittances, low refractive indices,and good adhesion to glass or polymer panes. Both treatments are madeand combined in order to fulfil the security requirements for facadeapplications, but also to provide some advantages. First of all, thelamination can offer the possibility to have different supply chains forcoating and etching, depending on the chosen configuration (see FIGS. 3and 4) thus offering a wide time savings. Moreover the coloured coatingis encapsulated, avoiding any colour change due to water condensation onthe inner side of the glazing when mounted on thermal collectors.

Another advantage is the good mechanical strength of the laminatedglazing which offers:

-   -   The possible use of glazing larger than the solar thermal or PVT        systems which can be directly bonded to the back of the glazing        and thus be completely hidden. Since the coloured coating is        encapsulated, such collectors can be obtained without any colour        change along the glued collector frame (which is the case when        the interferential coating is in direct contact with lamination        polymer or glue). Thermal, PV and PVT systems have therefore        exactly the same external appearance.    -   The possible use of the glass for the mechanical fixation of the        solar devices.

These capabilities allow the production of polyvalent products whichprovide considerable flexibility for roof and facade installation. Asexample, FIG. 28 presents possible variations for the mounting ofthermal solar systems glued behind a coloured laminated glazing. In FIG.28 a), solar thermal collectors are glued on the back of laminatedglazing larger than the frame of the collectors. Here the solarcollectors are mounted on a roof with glazing overlap and thewaterproofing is provided by the presence of seals between twooverlapping glazings. Different variations for the mounting of solarthermal collectors in ventilated facade either for residential facade orfor large buildings with glass facades are shown respectively in FIG. 28(b) and (c). Here, the hangers, the overlap wings, the seals and so oncan be adaptable to the wishes of the architect, the type andrequirements of the building, the local culture of the country, . . .Same mounting configurations are of course possible for photovoltaicdevices, but also for hybrid (combination of thermal and PV devices)roof and facades installations.

4. Optional Anti-Reflection Coating

In order to increase the solar transmittance of solar thermal devices ananti-reflection coating can be applied to the back-side of the innerglass (see FIG. 3).

As a matter of facts, a maximum transmittance value of approximately 92%can be achieved for the best quality glass as a reflectance of 4% onboth sides of the glass occurs. By applying an anti-reflection coatingcharacterised by a low refractive index (lower than 1.52) thereflectance of the glass side can be reduced of approximately 3% in thebest case.

Ideally, the solar transmittance of the coloured laminated glazing canthen increase of approx. 3% and thus compensating the transmittancelosses due to the presence of the interferential coloured coating.

REFERENCES

-   [1] H. A. McLeod, Thin Film Optical Filters, American-Elsevier, New    York, 1969.-   [2] International Commission on Illumination CIE, 1986. Colorimetry.    CIE Publication 15.2., 2nd ed., ISBN 3-900-734-00-3, Vienna-   [3] CIE Technical Report (2004) Colorimetry, 3rd ed. Publication    15:2004-   [4] M. Munari Probst and C. Roecker, “Towards an improved    architectural quality of building integrated solar thermal systems    (BIST),” Solar Energy, vol. 81, September 2007, pp. 1104-1116.-   [5] A. Schiller, C. Roecker, J.-L. Scartezzini, J. Boudaden, I. R.    Videnovic, R. S.-C. Ho, P. Oelhafen, Sol. Energy Mater. Sol. Cells    84 (2004) 241.-   [6] J. Boudaden, R. S. C. Ho, P. Oelhafen, A. Schiller, C. Roecker,    J.-L. Scartezzini, Solar Energy Materials & Solar Cells 84, 225    (2004).-   [7] A. Schüler, C. Roecker, J. Boudaden, P. Oelhafen, J.-L.    Scartezzini, Solar Energy 79, 122 (2005).-   [8] A. Schüler, J. Boudaden, P. Oelhafen, E. De Chambrier, C.    Roecker, J.-L. Scartezzini, Solar Energy Materials & Solar Cells 89,    219 (2005).-   [9] A. Schiller, PCT International Publication WO 3004/079278 A1    (2004).-   [10] H. Niederprüm, H. G. Klein, J.-N. Meussdoerffer, U.S. Pat. No.    4,055,458 (1977).-   [11] N. Enjo, K. Tamura, U.S. Pat. No. 4,582,624 (1986).-   [12] G. E. Blonder, B. H. Johnson, M. Hill, U.S. Pat. No. 5,091,053    (1992).-   [13] D. C. Zuel, J.-H. Lin, U.S. Pat. No. 5,120,605 (1992).-   [14] S. H. Gimm, J. H. Kim, US Patent 5281350 (1994).-   [15] H. Miwa, U.S. Pat. No. 7,276,181 B2 (2007).

LIST OF FIGURE CAPTIONS

FIG. 1:

Angular dependency of 1931 CIE (x, y) colour coordinates under CIE-D65illuminant of the coloured design given in Example 1.

FIG. 2:

Reflectance curves of the coating design given in Example 1 for variousangles of reflection (from 0° to 85°).

FIG. 3:

Schematic drawings of possible configurations of coloured laminatedglazing for thermal and PVT applications. The coloured coating can bedeposited (a) on the back side of the outer glass, (b) on one side of apolymeric film which is encapsulated between two glass panes, (c) on thefront side of the inner glass.

FIG. 4:

Schematic drawings of possible configurations of coloured laminatedglazing for PV applications. The coloured coating can be deposited (a)on the back side of the outer glass, (b) on one side of a polymeric filmwhich is encapsulated between two glass panes, (c) on the front side ofthe inner glass. Here the technical parts of the PV device are fullyintegrated into the laminated glazing.

FIG. 5:

1988 C.I.E. normalised photopic luminous efficiency function delimitingthe part of the solar spectrum which is visible for the human eye andreflectance curve at normal incidence (angle of vision of 0°) of ayellow-green coating (λ_(max)=570 nm) presenting a single reflectionpeak.

FIG. 6:

1988 C.I.E. normalised photopic luminous efficiency function delimitingthe part of the solar spectrum which is visible for the human eye andreflectance curve at normal incidence (angle of vision of 0°) of a greencoating (λ_(D)=500 nm) presenting three reflection peaks in the visiblepart of the solar spectrum (bulk part of the curve).

FIG. 7:

(a) Reflectance curves of a yellow-green coating for various angles ofreflection (from 0° to 85°). The reflection peak situated in the visiblepart of the spectrum shifts to smaller wavelengths: λ_(max) varies fromλ_(max 0°)=570 nm to λ_(max 60°)=500 nm leading to a colour change ofthe coating from yellow-green to green.

(b) Same representation for a green coating design presenting threereflection peaks in the visible part of the solar spectrum.

FIG. 8:

(a) Graphical representation of a fictive reflectance curve composed bytwo reflection peaks in the visible part of the solar spectrum. λ₁, C₁and λ₂, C₂ are the wavelengths and colours of the reflectance peaks atlow viewing angle. λ_(1′), C_(1′) and λ_(2′), C_(2′) are thecorresponding wavelengths and colours at higher angle of observation.The dominant colour M_(D) of the coating is situated at λ_(D) comprisedbetween λ₁ and λ₂, its position depending on the relative intensity ofboth reflection peaks.

(b) Principle of colour stability represented on the 1931 C.I.E.chromaticity diagram. M is the resultant colour of a coatingcharacterised by 2 reflection peaks, in the visible part of the solarspectrum, defined by C₁ and C₂ at low angle of vision. C_(1′) and C_(2′)are the corresponding colours for higher angle of vision. M_(D) is thedominant colour of M.

FIG. 9:

(a) Graphical representation of a fictive reflectance curve composed bythree reflection peaks in the visible part of the solar spectrum. λ₁,C₁, λ₂, C₂ and λ₃, C₃ are the wavelengths and colours of the reflectancepeaks at low viewing angle. λ_(1′), C_(1′), λ_(2′), C_(2′) and λ_(3′),C_(3′) are the corresponding wavelengths and colours at higher angle ofobservation. The dominant colour M_(D) of the coating is situated atλ_(D) whose position depends on the relative intensity of all reflectionpeaks.

(b) Principle of colour stability represented on the 1931 C.I.E.chromaticity diagram. M is the resultant colour of a coatingcharacterised by 3 reflection peaks, in the visible part of the solarspectrum, defined by C₁, C₂ and C₃ at low angle of vision. C_(1′),C_(2′) and C_(3′) are the corresponding colours for higher angle ofvision. M_(D) is the dominant colour of M.

FIG. 10:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65illuminant of the coloured design given in Example 2.

FIG. 11:

Reflectance curves of the coating design given in Example 2 for variousangles of reflection (from 0° to 85°).

FIG. 12:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65illuminant of the coloured design given in Example 3.

FIG. 13:

Reflectance curves of the coating design given in Example 3 for variousangles of reflection (from 0° to 85°).

FIG. 14:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65illuminant of the coloured design given in Example 4.

FIG. 15:

Reflectance curves of the coating design given in Example 4 for variousangles of reflection (from 0° to 85°).

FIG. 16:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65illuminant of the coloured design given in Example 5.

FIG. 17:

Reflectance curves of the coating design given in Example 5 for variousangles of reflection (from 0° to 85°).

FIG. 18:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65illuminant of the coloured design given in Example 6.

FIG. 19:

Reflectance curves of the coating design given in Example 6 for variousangles of reflection (from 0° to 85°).

FIG. 20:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65illuminant of the coloured design given in Example 7.

FIG. 21:

Reflectance curves of the coating design given in Example 7 for variousangles of reflection (from 0° to 85°).

FIG. 22:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65illuminant of the coloured design given in Example 8.

FIG. 23:

Reflectance curves of the coating design given in Example 8 for variousangles of reflection (from 0° to 85°).

FIG. 24:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65illuminant of the coloured design given in Example 9.

FIG. 25:

Reflectance curves of the coating design given in Example 9 for variousangles of reflection (from 0° to 85°).

FIG. 26:

Normal hemispherical transmittance measurements of a glass etched bysolution 1 (ABF/IPA/H₂O=30/10/60−15 min etch time), a glass etched bysolution 2 (ABF/sucrose/H₂O=18/18/64−15 min etch time) and an untreatedglass. The normal hemispherical transmittance is around 95% for bothetched glasses and around 92% for the untreated glass.

FIG. 27:

SEM pictures of glass surfaces structured by ABF-based etchingsolutions:

(a) ABF/IPA/H₂O=30/10/60−15 min etch time

(b) ABF/sucrose/H₂O=18/18/64−15 min etch time.

FIG. 28:

Possible variations for the mounting of thermal or PVT solar systemsglued behind a coloured laminated glazing: (a) example of roofinstallation with glazing overlap, (b) example of installation forresidential ventilated facade, (c) example of adaptation to largebuildings with glass facades.

EXAMPLES OF COATING DESIGNS Example 1

air//136 nm of L/222 nm of H//glass//222 nm of H/136 nm of L//air withn_(H)=1.54 and n_(L)=1.8

Example 2

air//glass//30 nm of H/25 nm of L/320 nm of H//polymer with n_(H)=2.4and n_(L)=1.65

Example 3

air//glass//185±12 nm of H/25±12 nm of L/35±12 nm of H/35±12 nm ofL/130±12 nm of H//polymer with n_(H) =2.4 and n_(i), =2.0

Example 4

air//glass//160±12 nm of H/130±12 nm of L/65±12 nm of H/25±12 nm ofL/70±12 nm of H/160±12 nm of L/100±12 nm of H//polymer with n_(H)=2.2and n_(L)=2.0

Example 5

air//glass//45±12 nm of H/70±12 nm of L/45±12 nm of H//polymer withn_(H)=2.0 and n_(L)=1.65

Example 6

air//glass//175±12 nm of H/85±12 nm of L/50±12 nm of H/25±12 nm ofL/300±12 nm of H//polymer

with n_(H)=2.4 and n_(L)=2.0

Example 7

air//glass//120±12 nm of H/120±12 nm of L/95±12 nm of H/90±12 nm ofL/90±12 nm of H/95±12 nm of L/100±12 nm of H//polymer with n_(H)=2.0 andn_(L)=1.65

Example 8

air//glass//40±12 nm of H/75±12 nm of L//polymer with n_(H)=2.4 andn_(L)=1.65

Example 9

air//glass//50±12 nm of H/90±12 nm of L/65±12 nm of H/55±12 nm ofL//polymer with n_(H)=2.4 and n_(L)=2.0

1-24. (canceled)
 25. A laminated glazing unit for architecturalintegration of solar energy systems comprising a substrate delimited bytwo main faces and a multi-layered interference filter also delimited bytwo main faces and being adapted to be in contact on one main face withsaid substrate and on the other main face with a laminating polymer;said substrate being in contact with an incident medium having arefractive index n_(inc)=1 and having a refractive index n_(inc)substrate defined as follows: 1.45≦n_(substrate)≦1.6 at 550 nm and; saidlaminating polymer being considered as the exit medium whose refractiveindex is defined as follows 1.45≦n_(exit)≦1.6 at 550 nm; and whereinsaid unit is designed in such a way that the following requirements aremet: 1a) The saturation of the colour, given by C*_(ab)=√(a*)²+(b*)²,according to the CIE colour coordinates L*, a* and b* under daylightillumination CIE-D65 is higher than 8 at near-normal angle ofreflection, except for grey and brown. 1b) The visible reflectance atnear-normal angle of reflection R_(vis) is higher than 4%. 1c) Thevariation of the dominant wavelength λ_(MD) of the dominant colour M_(D)of the reflection with varying angle of reflection θr is smaller than 15nm for θr<60°. 1d) The total hemispherical solar transmittance atnear-normal incidence is above 80%.
 26. The glazing unit according toclaim 25 comprising a light-diffusing rough outer surface obtained bychemical treatment such as for example acid etching.
 27. The glazingunit according to claim 25 using acidic etching treatment leading toanti-reflective properties of the outer surface and thus enhancing theoptical properties of the system: the solar transmittance of a lightbeam at normal incidence is approx. 3% higher for the etched surfacethan for an untreated surface.
 28. The glazing unit according to claim25 with optional anti-reflective coating applied on the back-side of thelaminated glazing in order to enhance the optical properties of thesystem for solar thermal applications: the solar transmittance of alight beam at normal incidence is approx. 3% higher for the surface onwhich the anti-reflective coating is applied than for an untreatedsurface.
 29. The glazing unit according to claim 25 comprising solarroll glass, an extra-white float glass (iron content <120 ppm) orpolymeric materials (PET, PEN, PFA, FEP, ETFE, PTFE . . . )characterised by a solar transmittance higher than 90%.
 30. The glazingunit according to claim 25 where solar roll glass surfaces is eitherflat or textured.
 31. The glazing unit according to claim 25 usingelastomer cross-linking polymers such as EVA, thermoplastic productssuch as PVB, or ionoplastic polymers to join the glass or polymericpanes together by lamination and where the solar transmittance of theunit is higher than 92% for a polymer thickness of 0.4-0.5 mm.
 32. Theglazing unit according to claim 25, wherein said interferential filteris a multilayer interferential stack of up to 9, up to 400 nm-thickdielectric layers with low absorption expressed by the extinctioncoefficient k≦0.2 for wavelengths λ with 450 nm≦λ≦2500 nm.
 33. Theglazing unit according to claim 25, wherein said interference filter hasa green coloured reflection deposited on a glass or polymer substratewith 1.45≦n_(substrate)≦1.6 at 550 nm and composed by 3 sub-layers basedon low refractive index material L with 1.4≦nL≦2.2 at 550 nm and highrefractive index material H with 1.8≦n_(H)≦2.5 at 550 nm; the generaldesign being: incident medium air//substrate//30±12 nm of H/25±12 nm ofL/320±12 nm of H///exit medium polymer.
 34. The glazing unit accordingto claim 25, wherein said interference filter has a green colouredreflection deposited on a glass or polymer substrate with1.45≦n_(substrate)≦1.6 at 550 nm and composed by 5 sub-layers based onlow refractive index material L with 1.4≦n_(L)≦2.2 at 550 nm and highrefractive index material H with 1.8≦n_(H)≦2.5 at 550 nm; the generaldesign being: incident medium air//substrate//185±12 nm of H/25±12 nm ofL/35±12 nm of H/35±12 nm of L/130±12 nm of H//exit medium polymer. 35.The glazing unit according to claim 25, wherein said interference filterhas a green coloured reflection deposited on a glass or polymersubstrate with 1.45≦n_(substrate)≦1.6 at 550 nm and composed by 7sub-layers based on low refractive index material L with 1.4≦n_(L)≦2.2at 550 nm and high refractive index material H with 1.8≦n_(H)≦2.5 at 550nm; the general design being: incident medium air//substrate//160±12 nmof H/130±12 nm of L/65±12 nm of H/25±12 nm of L/70±12 nm of H/160±12 nmof L/100±12 nm of H//exit medium polymer.
 36. The glazing unit accordingto claim 25, comprising an interference filter with blue colouredreflection deposited on glass or polymer substrate with1.45≦n_(substrate)≦1.6 at 550 nm and composed by 3 sub-layers based onlow refractive index material L with 1.4≦n_(L)≦1.8 at 550 nm and highrefractive index material H with 1.8≦n_(H)≦2.5 at 550 nm; the multilayerdesign corresponding hereby to: incident medium air//substrate/45±12 nmof H/70±12 nm of L/45±12 nm of H//exit medium polymer.
 37. The glazingunit according to claim 25, comprising an interference filter withyellow-green coloured reflection deposited on glass or polymer substratewith 1.45≦n_(substrate)≦1.6 at 550 nm and composed by 5 sub-layers basedon low refractive index material L with 1.65≦n_(L)≦2.1 at 550 nm andhigh refractive index material H with 1.8≦n_(H)≦2.5 at 550 nm; themultilayer design corresponding hereby to: incident mediumair//substrate/175±12 nm of H/85±12 nm of L/50±12 nm of H/25±12 nm ofL/300±12 nm of H//exit medium polymer.
 38. The glazing unit according toclaim 25, comprising an interference filter with yellowish-orangecoloured reflection deposited on glass or polymer substrate with1.45≦n_(substrate)≦1.6 at 550 nm and composed by 7 sub-layers based onlow refractive index material L with 1.4≦n_(L)≦1.8 at 550 nm and highrefractive index material H with 1.8≦n_(H)<2.5 at 550 nm; the multilayerdesign corresponding hereby to: incident medium air//substrate/120±12 nmof H/120±12 nm of L/95±12 nm of H/90±12 nm of L/90±12 nm of H/95±12 nmof L/100±12 nm of H//exit medium polymer.
 39. The glazing unit accordingto claim 25, comprising an interference filter with grey colouredreflection deposited on glass or polymer substrate with1.45≦n_(substrate)≦1.6 at 550 nm and composed by 2 sub-layers based onlow refractive index material L with 1.4≦n_(L)≦1.8 at 550 nm and highrefractive index material H with 1.8≦n_(H)≦2.5 at 550 nm; the multilayerdesign corresponding hereby to: incident medium air//substrate//40±15 nmof H/75±30 nm of L//exit medium polymer.
 40. The glazing unit accordingto claim 25, comprising an interference filter with brown colouredreflection deposited on glass or polymer substrate with1.45≦n_(substrate)≦1.6 at 550 nm and composed by 4 sub-layers based onlow refractive index material L with 1.65≦n_(L)≦2.1 at 550 nm and highrefractive index material H with 1.8≦n_(H)≦2.5 at 550 nm; the multilayerdesign corresponding hereby to: incident medium air//substrate//50±12 nmof H/90±12 nm of L/65±12 nm of H/55±12 nm of L//exit medium polymer. 41.The glazing unit according to claim 25, comprising one or more glasspane(s) being heat treated (heat-strengthened or fully tempered) forsecurity in façade applications.
 42. A solar energy system comprising alaminated glazing according to claim
 25. 43. The solar energy systemaccording to claim 42 comprising a thermal collector and wherein theglazing is directly glued to the solar thermal collector.
 44. The solarenergy system according to claim 43 wherein the solar glazing is largerthan the frame of the collector.
 45. The solar energy system accordingto claim 42 comprising a PV system with an active system (silicon cells,PV thin films, contacts, back-reflector . . . ) fully integrated in thelaminated glazing.
 46. The solar roof or building façade comprising asolar energy system according to claim
 42. 47. The solar roof orbuilding façade according to claim 25 where the solar energy system issuspended by fixations attached to the glazing.
 48. The solar roof orbuilding façade according to claim 46 with an overlapping of thelaminated glazing.